1. Field of the Invention
The present invention relates to a semiconductor integrated circuit.
2. Description of the Related Art
A variety of wireless systems such as cellular phones and wireless LAN has been developed in recent years. Multiple frequency bands have been provided to increase channel capacity, even with the same radio system, and because of national circumstances. An apparatus for providing service to such multiple frequency bands must have a radio frequency integrated circuit (RFIC) for supporting each frequency band. Either a frequency band tuning circuit or multiple high frequency circuits are required to realize a radio frequency integrated circuit for supporting each frequency band. In this way, a single chip can be given the ability to use multiple frequency band circuits by having either a circuit for tuning multiple frequency bands or multiple high frequency circuits and connecting only to the circuit that is appropriate for the frequency band being used. The size of a single chip, however, will increase in cases such as this. Passive circuits comprising capacitors and inductors occupy an especially large area compared to circuits comprising elements such as transistors inside an IC chip. Frequency band tuning circuits include capacitors or inductors, so if multiple frequency band tuning circuits are provided in an IC chip, the chip size will be greater than would be the case so that multiple elements such as transistors were provided.
FIGS. 8, 9, 10, 11A, 11B, and 11C show the problems of conventional art.
FIG. 8 shows the configuration of a typical high frequency circuit. FIG. 9 shows the first configuration of a conventional RFIC which can support broadband. FIG. 10 shows the second configuration of a conventional RFIC which can support broadband. FIGS. 11A, 11B, and 11C show three configurations of a conventional RFIC which can support broadband.
As shown in FIG. 8, a high frequency circuit 11 provides an input matching circuit 10 and an output matching circuit 12 for tuning to the desired frequency band. Because matching circuits have specific frequency characteristics (filter characteristics), they cannot realize broadband frequency circuits which cover multiple frequency bands with a single matching circuit.
As shown in FIG. 9, variable capacitors or variable inductors may be provided between the input matching circuit 10 and the output matching circuit 12 to produce a broadband RFIC, which includes high frequency circuits. In this circuit, variable capacitors or variable inductors are used to make the operating frequency of matching circuits variable. However, passive components such as capacitors or inductors increase the area of RFICs more than any other elements in an IC.
Also, as described in Japanese Unexamined Patent Application Publication No. 2004-350117 or Japanese Unexamined Patent Application Publication No. 2006-12990, there are cases where transistor switches are used to make inductors or capacitors variable. However, because the ON resistance of transistors is several tens of ohms, significant degradation of performance characteristics may occur in high frequency circuits. It is also difficult to actually apply the transistors RFICs which handle high frequency signals can not realize a variable matching circuit in this way.
Also, as shown in FIG. 10, there is a method whereby only the high frequency circuit 11 is provided in an RFIC. An outside RFIC comprises external matching circuits 10a and 12a as discrete components. The external matching circuits 10a and 12a are connected to the RFIC by wires. Also, if variable matching circuits 10a and 12a are provided outside the RFIC, an IC comprised of variable capacitors or variable inductors will be configured as discrete components with a large area. Therefore, the resulting IC becomes larger, which has more components, which becomes more expensive, and which has a larger circuit size.
Furthermore, as shown in FIGS. 11A, 11B, and 11C, when a single IC provides multiple high frequency circuits to cover each frequency band, the number of circuits increases. The RFIC area, in particular, increases due to active components such as inductors or capacitors that are used in matching circuits.